KR100960836B1 - Multi-antenna station with distributed antennas - Google Patents

Multi-antenna station with distributed antennas Download PDF

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Publication number
KR100960836B1
KR100960836B1 KR20087000059A KR20087000059A KR100960836B1 KR 100960836 B1 KR100960836 B1 KR 100960836B1 KR 20087000059 A KR20087000059 A KR 20087000059A KR 20087000059 A KR20087000059 A KR 20087000059A KR 100960836 B1 KR100960836 B1 KR 100960836B1
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South Korea
Prior art keywords
antennas
antenna
terminal
selecting
access point
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KR20087000059A
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Korean (ko)
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KR20080016928A (en
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수브라만얌 드라비다
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퀄컴 인코포레이티드
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04W—WIRELESS COMMUNICATION NETWORKS
    • H04W88/00—Devices specially adapted for wireless communication networks, e.g. terminals, base stations or access point devices
    • H04W88/08—Access point devices
    • H04W88/085—Access point devices with remote components
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B7/00—Radio transmission systems, i.e. using radiation field
    • H04B7/02—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas
    • H04B7/04—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas
    • H04B7/06—Diversity systems; Multi-antenna system, i.e. transmission or reception using multiple antennas using two or more spaced independent antennas at the transmitting station
    • H04B7/0686—Hybrid systems, i.e. switching and simultaneous transmission
    • H04B7/0691—Hybrid systems, i.e. switching and simultaneous transmission using subgroups of transmit antennas

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Mobile Radio Communication Systems (AREA)
  • Time-Division Multiplex Systems (AREA)

Abstract

A multi-antenna station is described that has a distributed antenna and can provide good performance for a terminal distributed over the coverage area of the multi-antenna station. The multi-antenna station includes a plurality of antennas, a controller, and one or more transmitter units. The multiple antennas include one or more remote antennas coupled to the multi-antenna station and located away from the multi-antenna station. The controller selects a set of one or more antennas from among the multiple antennas for data transmission to the terminal. One or more transmitter units transmit data to the terminal via a set of one or more antennas.

Multi Antenna Station, Remote Antenna, Power Detector, Power Threshold, Location Information

Description

MULTI-ANTENNA STATION WITH DISTRIBUTED ANTENNAS

background

I. Field

TECHNICAL FIELD This disclosure relates generally to communications and, more particularly, to multi-antenna stations.

II. background

A wireless local area network (WLAN) has one or more access points serving one or more user terminals. The number of access points and the number of user terminals depend on the size of the WLAN. For example, a single access point may serve multiple user terminals distributed throughout a WLAN deployment area, which may be an entire building, a floor of a building, or the like. While common, but the access point is fixed, the performance achieved by each user terminal usually depends on the location of each user terminal relative to the access point. It is well understood that radio frequency (RF) signals are degraded by obstructions (eg walls) and artifacts (eg noise and interference) in the signal path between the transmitter and receiver. Thus, a nearby user terminal located in proximity to the access point and in the line of sight of the access point may achieve better performance than a remote user terminal located far from the access point and not in the visible range of the access point. have. As a result, different levels of performance (eg, different data rates) are achievable for different user terminals, which are usually located in different parts of the WLAN deployment area.

It is desirable to provide similar levels of performance to all user terminals or as many user terminals as possible within a WLAN deployment area. Thus, there is a need in the art for an access point capable of providing such a similar level of performance to a user terminal.

summary

Within this specification, a multi-antenna station is described that has a distributed antenna and can provide good performance for terminals distributed across the coverage area of the multi-antenna station. In accordance with an embodiment of the present invention, a multi-antenna station is described that includes multiple antennas, controllers, and one or more transmitter units. The multiple antennas include one or more remote antennas coupled to the multi-antenna station and positioned away from the multi-antenna station. The controller selects a set of one or more antennas from among the multiple antennas for data transmission to the terminal. One or more transmitter units transmit data to the terminal via a set of one or more antennas.

According to another embodiment, a method is provided wherein a set of one or more antennas from among multiple antennas is selected for data transmission from a multi-antenna station to a terminal. The multiple antennas include one or more remote antennas located away from the multi-antenna station. Data is transmitted to the terminal via a set of one or more antennas.

According to yet another embodiment, an apparatus is described comprising means for selecting a set of one or more antennas among a plurality of antennas for data transmission to a terminal and means for transmitting data to the terminal via the set of one or more antennas. Here, the plurality of antennas includes one or more remote antennas located away from the device.

Various aspects and embodiments of the invention are described in further detail below.

Brief description of the drawings

1 illustrates a WLAN with a single access point and multiple user terminals.

2A to 2D are diagrams showing four antenna configurations for the access point.

3 is a diagram illustrating a process performed by an access point to transmit data to and receive data from a user terminal.

4 is a block diagram of an access point.

5A and 5B show two embodiments of a remote front end.

details

The word "exemplary" is used herein to mean "acting as an example, illustration, or illustration." Any embodiment described herein as "exemplary" is not necessarily to be construed as preferred or advantageous over other embodiments.

1 is a diagram illustrating an exemplary WLAN 100 having a single access point (AP) 110 serving multiple user terminals (UT) 120. Access point 110 is a multi-antenna station with multiple antennas that may be used for data transmission and reception. An access point may also be called a base station, Node B, or some other terminology. Each user terminal 120 may be provided with a single antenna or multiple antennas. A user terminal may also be called a mobile station, user equipment, wireless device, or some other terminology.

Access point 110 may send a multiple input multiple output (MIMO) transmission to a multi antenna user terminal, or may transmit a multiple input single output (MISO) transmission to a single antenna user terminal. Access point 110 may also receive a MIMO transmission from a multi-antenna user terminal or may receive a single input multiple output (SIMO) transmission from a single antenna user terminal. The MIMO channel formed by multiple (N T ) transmit antennas at the transmitter and multiple (N R ) receive antennas at the receiver is N S (where N S ≤ min {N T , N R }) may be resolved into spatial channels. The N S spatial channel may be used to transmit data in parallel to achieve higher throughput, and / or to transmit data in duplicate to achieve greater reliability. The MISO channel formed by multiple transmit antennas and a single receive antenna consists of a single spatial channel. Multiple transmit antennas may be used to transmit data in a manner that improves reliability. The SIMO channel formed by a single transmit antenna and multiple receive antennas also consists of a single spatial channel. Multiple receive antennas may be used to receive data in a manner that improves reliability.

The access point 110 may be a fixed station and may be located at any location within the WLAN deployment area, which may be a building, a floor of a building, a house, an office complex, a store, or the like. User terminal 120 may be distributed throughout the WLAN deployment area. Some user terminals (eg, user terminals 120c and 120d) may be located in proximity to the access point 110, while some other user terminals (eg, user terminals 120a and 120b) It may be located far from the access point 110. Each user terminal 120 may be fixed or mobile. Usually, within the WLAN deployment area, there are obstacles (eg, walls) that degrade the RF signal transmitted between the access point 110 and the user terminal 120. There may be other artifacts (eg, interference) that may further degrade the RF signal. These obstructions and artifacts are not shown in FIG. 1 for simplicity.

In order to provide good performance for all user terminals 120 or multiple user terminals 120, multiple antennas of the access point 110 are distributed throughout the WLAN deployment area. Access point 110 has L local antennas 112a-112l mounted on or close to the access point. In general, L may be 0, 1 or more than 1, ie L ≧ 0. The access point 110 further has M remote antennas 114a-114m disposed at different locations throughout the WLAN deployment area. The remote antennas 114 may be disposed at different distances from the access point 110, may be disposed at different angular positions with respect to the access point 110, and so on. In general, M is at least 1, ie M ≧ 1. The total number of local and remote antennas available for use by the access point 110 is N ap (ie, N ap = L + M ≧ 2).

Various types of antennas may be used for the local antenna 112 and the remote antenna 114, which may also be called an access point (AP) antenna. For example, each AP antenna may be a cross-pole antenna, a dipole antenna, a patch antenna (or chip), or the like. The antenna may also be called an antenna element, a radiation element, or the like. Each AP antenna is scheduled for the operating frequency band used for WLAN 100. Each AP antenna may also have any radiation pattern. The radiation pattern and antenna type for each AP antenna may be selected based on the coverage area intended for that AP antenna. For example, an omnidirectional radiation pattern antenna may be used for the remote antenna 114d located near the middle of the WLAN deployment area of FIG. 1, and the antenna of the directional radiation pattern may be located at the corner of the WLAN deployment area. It may be used for located remote antennas 114a, 114c, 114e and 114n.

In the embodiment shown in FIG. 1, each remote antenna 114 is an individual remote that performs signal conditioning (eg, amplification, filtering, etc.) on the RF signals transmitted and received via its respective remote antenna. Coupled to a front end (RFE) 116. Some embodiments of RFE 116 are described below. The RFE 116 for each remote antenna 114 is coupled to the access point 110 via a cable 118. The cable 118 may be a coaxial cable usually used for cable television, or may be some other type of cable that supports an operating frequency band for the WLAN 100. Cable 118 may also be replaced with other types of communication links (eg, RF, infrared, etc.). The RFE 116 can reduce signal loss due to the cable 118, thereby improving performance. In general, RFE 116 may or may not be used for each remote antenna 114.

The local antenna and remote antenna for the access point 110 may be arranged and selected in various ways. Some exemplary configurations of local and remote antennas are described below. Some exemplary embodiments of selecting an antenna for data transmission are also described below.

FIG. 2A is a diagram showing an access point 110a without a local antenna and having a large number (M > 1) of remote antennas 114a to 114m. Access point 110a is an embodiment of access point 110 in FIG. 1 and has N ap = M antennas available for data transmission and reception. Each remote antenna 114 is coupled to the access point 110a via an associated RFE 116 and cable 118. In the embodiment shown in FIG. 2A, each remote antenna 114 is coupled to a respective power detector 290 in the access point 110a. Each power detector 290 measures the power of the RF signal received by the associated antenna and provides a power measurement to the controller 220. The controller 220 uses the power measurements from all power detectors 290 to select an antenna for data transmission and reception.

FIG. 2B shows an access point 110b having a single (L = 1) local antenna 112 and multiple (M> 1) remote antennas 114a-114m. Access point 110b is another embodiment of access point 110 in FIG. 1 and has N ap = M + 1 antennas available for data transmission and reception. In the embodiment shown in FIG. 2B, each of the M + 1 antennas is coupled to an individual power detector 290 within the access point 110. Controller 220 receives power measurements from all power detectors 290 and selects antennas for data transmission and reception.

2C is a diagram showing an access point 110c having multiple (L> 1) local antennas 112a to 112l and multiple (M> 1) remote antennas 114a to 114m. Access point 110c is another embodiment of access point 110 in FIG. 1 and has N ap = L + M antennas available for data transmission and reception. In general, L may be the same as M or may not be the same.

In the embodiment shown in FIGS. 2A-2C, each of the N ap antennas available at the access point may be individually selected for data transmission and / or data reception. Controller 220 may select one antenna, a subset of available antennas, or all of the available antennas for data transmission to a given user terminal and / or for receiving data from that given user terminal. Controller 220 may select an antenna based on power measurements for the available antennas, as described below.

FIG. 2D is a diagram showing an access point 110d having multiple (M> 1) local antennas 112a to 112m and multiple (M) remote antennas 114a to 114m. Access point 110d is another embodiment of access point 110 in FIG. 1 and has N ap = 2M antennas available for data transmission and reception. In the embodiment shown in FIG. 2D, each local antenna 112 is associated with one remote antenna 114. M pairs of antennas with M local antennas 112 and M remote antennas 114 are formed. In an embodiment, the controller 220 selects one or more antenna pairs for data transmission to a given user terminal and also, for example, based on power measurements for two antennas of each selected pair, respectively. Select one antenna from the selected pair.

The WLAN 100 may impose a condition that at most N antennas, where N may be equal to 2, 4, or some other value, may be used for data transmission. WLAN 100 may also support multiple transmission modes. Each transmission mode may require some minimum number of antennas or a certain number of antennas for data transmission using the transmission mode, as described below. For simplicity, the following description assumes that the access point 110 can select up to N antennas for data transmission to a given user terminal. The access point 110 also selects a transmission mode to use for data transmission based on the number of antennas selected. The access point 110 may select an antenna for data transmission to the user terminal in various ways.

In an embodiment, the access point 110 selects N (where N < N ap ) antennas with the best power measurements for data transmission to the user terminal. In the embodiment shown in FIGS. 2A-2C, access point 110 receives power measurements for N ap available antennas, classifies the power measurements (eg, from highest to lowest), Select N antennas with the N best power measurements. In the embodiment shown in FIG. 2D, the access point 110 selects the N best pair of antennas based on its power measurements and selects the better antenna of the two antennas of each pair.

In another embodiment, the access point 110 selects up to N antennas with power measurements that exceed a predetermined power threshold P th . The access point 110 compares the power measurement for each antenna with the power threshold, retains the antenna if its power measurement exceeds the power threshold, and otherwise abandons the antenna. Access point 110 selects the N best antennas if more than N antennas have power measurements that exceed a power threshold. The access point 110 may select less than N antennas only if the power measurements for these antennas exceed the power threshold. The access point 110 may select the best available antenna or a predetermined number of best antennas if no antenna has power measurements that exceed the power threshold.

In another embodiment, the access point 110 initially selects the N best antennas with the best power measurements and then gives up all antennas with a small contribution to data transmission to the user terminal. Such antenna pruning may be achieved as follows. The access point 110 arranges the N best antennas based on their power measurements, for example, from the highest power measurement P 1 to the lowest power measurement P N for the N antennas. The access point 110 then determines the power gap ΔP i between each two adjacently classified antennas i and i + 1 for the difference in their power measurements, or i = 1, ..., In the case of N-1, it is calculated as ΔP i = P i -P i + j . The access point 110 then determines whether the power gap ΔP i for any antenna pair exceeds a predetermined amount ΔP th , or i = 1, ..., N-1 If? P i >? P th , it is determined. If the amount exceeds the power gap (△ P j) for a given antenna j is determined in advance, the access point 110, and to give up all of the antennas with a power measurement of less than P j +1. This embodiment eliminates small antennas that contribute to data transmission sent to the user terminal, which reduces crosstalk between the antennas.

The above described embodiments relate to selecting an antenna based on power measurements available at the access point 110. The access point 110 may select antennas based on other parameters instead of or in addition to the received power. For example, access point 110 may include (1) a received signal-to-noise ratio (SNR) that is a desired signal (e.g., pilot) to a total noise and interference ratio, and (2) a received signal that is a desired signal to total received power ratio. The antenna may be selected based on strength, or (3) some other indication of the received signal quality. In the following description, antenna measurements may represent any type of measurement (eg, power, SNR, signal strength, etc.) suitable for use in selecting an antenna.

The access point 110 may also select an antenna based on other information available for the antenna. In an embodiment, the access point 110 selects an antenna based on the location information for the local antenna and the remote antenna. Each antenna may be associated with a set of one or more nearby antennas. This location information may be stored in a database. If high power measurements are obtained for a given antenna, the access point 110 may select one or more other antennas known to be located near this antenna. For example, if high power measurements are obtained for the remote antenna 114a of FIG. 1, the access point 110 may select the antenna 114b and / or antenna 114d for data transmission to the user terminal. have.

In another embodiment, the access point 110 selects an antenna based on the location information for the local antenna and the remote antenna. If the location of the local antenna and the remote antenna and the location of the user terminal are known, the access point 110 may select one or more antennas located near the user terminal. The position of the AP antenna may be identified and provided during deployment. The location of the user terminal may be approximated by measurements and / or may be confirmed in some other manner.

In yet another embodiment, the access point 110 selects an antenna based on correlation information for the local antenna and the remote antenna. Some antennas may have a high correlation, which results in excessive crosstalk and insufficient spatial separation between these antennas. As a result, antennas with high correlation should not be selected together. Correlation information for the available antennas may be ascertained based on placement, type, and / or measurements for the antennas. For example, local antennas 112 may have high correlation due to their close spacing, and it may be desirable to select only one local antenna or some local antenna for data transmission.

Access point 110 may also select an antenna based on information obtained from a higher layer above the physical layer in the protocol stack. The access point 110 usually transmits data in a packet to a user terminal. The user terminal may send back an acknowledgment (ACK) for each correctly decoded packet and a negative acknowledgment (NAK) for each error decoded packet. The access point 110 may initially select a set of antennas for data transmission to the user terminal, for example based on power measurements. If a large percentage of packets are decoded in error, the access point 110 may select a different set of antennas for data transmission to the user terminal.

The access point 110 may alternatively select antennas for data transmission to the user terminal, which is within the scope of the present invention. Access point 110 may select antennas based on any criteria or any combination of criteria.

Access point 110 may select different sets of antennas for data transmission to different user terminals, for example, based on measurements for these user terminals. Access point 110 may obtain measurements for each user terminal prior to data transmission to the user terminal and may select a set of antennas for the user terminal based on these measurements. This allows the access point 110 to use the best set of antennas for each data transmission.

Access point 110 may store the selected antenna set for each user terminal in the lookup table. This antenna set may be indexed by an identifier for the user terminal. This identifier may be a media access control identifier (MAC ID) that the access point 110 assigns to a user terminal at the beginning of a communication session, or may be some other type of identifier. Table 1 shows an example lookup table for the user terminals 120a-120d in the example shown in FIG. 1.

Figure 112008000167691-pct00001

Access point 110 may not have any measurements for a given user terminal at the beginning of data transmission to the user terminal. The access point 110 may then access a lookup table with the MAC ID of the user terminal to retrieve the set of antennas preselected for the user terminal. The access point 110 may use this preselected set of antennas to transmit data to the user terminal until the set is updated, for example with new measurements.

The access point 110 selects a first set of T antennas for downlink data transmission to the user terminal and selects a second set of R antennas for receiving uplink data transmission from the user terminal. . In general, N ≧ T ≧ 1, N ≧ R ≧ 1, and T may or may not be equal to R. R may also be larger than N if supported by spatial processing at access point 110, but this possibility is not described below for the sake of simplicity. The number T of transmit antennas depends on the number of good antennas available for downlink data transmission, the transmission mode used by the access point 110 for downlink data transmission, and possibly other factors. An antenna may be considered good if it passes one or more selection criteria, for example if its power measurement exceeds a power threshold. The number R of receive antennas depends on the number of good antennas available for uplink data reception, the transmission mode used by the user terminal for uplink data transmission, and possibly other factors.

The access point 110 may select the first set of T transmit antennas as described above, and may also select the second set of R receive antennas in a similar manner. The first set of antennas may be the same as or different from the second set of antennas. Processing at the access point 110 may be simplified by using a single antenna set for both data transmission and reception. In this case, each selected antenna is used to both transmit the RF signal to the user terminal, receive the RF signal from the user terminal, and so on.

3 is a diagram illustrating a process 300 performed by an access point 110 for transmitting data to and receiving data from a user terminal. For example, based on the pilot transmitted by the user terminal, measurements for the local antenna and the remote antenna at the access point 110 are obtained (block 310). The measurement may be for the received power and / or some other parameter. The first set of one or more (T) transmit antennas is based on a measurement and / or other information, from among N ap (where N ap > N ≧ T ≧ 1) antennas available at the access point 110. Is selected (block 312). Antenna selection may be performed in a variety of ways, as described above. If no measurements are available, a set of recently used antennas for data transmission to the user terminal may be retrieved from the lookup table and used for the current downlink data transmission. The transmission mode is selected for data transmission to the user terminal based on the number of selected transmission antennas.

A second set of one or more (R) receive antennas is also available based on the measurement and / or other information, where N ap (where N ap > N ≧ R ≧ 1) antennas is available. (Block 314). The first set and the second set may have the same or different number of antennas, for example, based on the transmission mode used for the downlink data transmission and the uplink data transmission. Although R = T, the second set may include the same or different antennas as the antenna in the first set.

The access point 110 processes the data according to the transmission mode selected for the downlink (block 316) and then transmits the processed data from the first set of T antennas to the user terminal (block 318). Access point 110 receives the uplink data transmission from the user terminal via the second set of R antennas (block 320).

Referring again to FIG. 1, the access point 110 may serve a number of user terminals 120 in the WLAN 100. Each user terminal 120 may need a specific set of transmit antennas for good downlink performance and a specific set of receive antennas for good uplink performance. Access point 110 may dynamically switch between sets of different antennas used for different user terminals such that each user terminal is serviced with a set of transmit / receive antennas that provide good performance for that user terminal. It may be. The electronics of the access point 110 may be designed to have the ability to quickly switch to different user terminals with different sets of antennas (eg, according to the principle per data packet, or the principle per frame). It may be.

4 is a diagram illustrating an embodiment of the access point 110. In this embodiment, the access point 110 includes a digital unit 210 that performs digital processing, and N transceivers 230a through 230n that perform signal conditioning on the RF and baseband signals for the N antennas. And an RF switch 280 that couples the N transceivers 230 to the N antennas selected from among N ap antennas available at the access point 110.

Each transceiver 230 includes a transmitter unit (TMTR) 240 and a receiver unit (RCVR) 260. The transmitter unit and receiver unit may be implemented in a super heterodyne structure or a direct conversion structure. In a super heterodyne architecture, frequency conversion between RF and baseband is performed in multiple stages, for example, from RF to intermediate frequency (IF) in one stage and from IF to baseband in another stage. In a direct conversion scheme, frequency conversion is performed directly in a single stage, for example from RF to baseband. For simplicity, FIG. 4 shows an embodiment of a transmitter unit 240 and a receiver unit 260 implemented in a direct conversion structure.

Within transmitter unit 240, digital-to-analog converter (DAC) 242 receives a stream of digital chips from digital portion 210 and converts the chips to analog to provide an analog baseband signal. Filter 244 then filters the analog baseband signal to remove the unwanted image generated by the digital-to-analog conversion to provide a filtered baseband signal. Amplifier 246 amplifies and buffers the filtered baseband signal to provide an amplified baseband signal. Mixer 248 modulates the TX_LO carrier signal from a voltage controlled oscillator (VCO; not shown in FIG. 4) into an amplified baseband signal to provide an upconverted signal. Power amplifier (PA) 250 amplifies the upconverted signal and provides an RF modulated signal to RF switch 280.

In the transmit path, the RF switch 280 receives up to N RF modulated signals from the transmitter units 240 of the N transceivers 230a-230n. The RF switch 280 also receives an Ant_Sel control signal indicating to which AP antenna the transceiver will be coupled. The RF switch 280 routes each received RF modulated signal to either the RFE 116 or the selected local antenna 112 for the selected remote antenna 114. In the receive path, the RF switch unit 280 receives an RF input signal from each remote antenna 114 and each local antenna 112 selected for data reception. The RF switch unit 280 routes each received RF input signal to the receiver unit 260 of the designated transceiver 230. The RF switch unit 280 may be implemented with a transmit / receive (T / R) switch, duplexer, or the like, as known in the art. The RF switch unit 280 does not need to have a separate transceiver 230 for each of the N ap antennas of the access point 110.

Within receiver unit 260, low noise amplifier (LNA) 262 receives an RF input signal from RF switch 280 for the selected AP antenna. LNA 262 amplifies the received RF signal to provide a conditioned RF signal with a desired signal level. Mixer 264 demodulates the conditioned RF signal into an RX_LO signal from the VCO to provide a down-converted signal. Filter 266 filters the downconverted signal to pass the desired signal components and remove noise and unwanted signals that may be generated by the frequency downconversion process. Amplifier 268 amplifies and buffers the filtered signal to provide an analog baseband signal. An analog-to-digital converter (ADC) 270 digitizes the analog baseband signal and provides a stream of samples to the digital portion 210.

In the embodiment shown in FIG. 4, the power detector 290 in the receiver unit 260 receives the conditioned RF signal from the LNA 262 and measures the power received in the conditioned RF signal to determine the power measurement. The main controller 220 in the digital unit 210 is provided. The power detector 290 may also measure the received power based on the baseband signal (eg, after the filter 266 or the amplifier 268). The power detector 290 may be implemented in a variety of ways, as known in the art.

4 shows an exemplary design for a transmitter unit and a receiver unit. In general, the transmitter unit and receiver unit may each include one or more stages, such as an amplifier, filter, mixer, or the like, which may be arranged differently from the configuration shown in FIG. 4. The transmitter unit and receiver unit may also include different elements and / or additional elements not shown in FIG. 4.

4 shows an embodiment of a digital portion 210 including various processing units that perform digital processing for data transmission and reception. Within digital unit 210, data processor 212 performs encoding, interleaving, and symbol mapping for data transmission, and symbol demapping, deinterleaving, and decoding for data reception. Spatial processor 214 performs transmitter spatial processing (e.g., beamforming, eigensteering, etc.) for data transmission, and receiver spatial processing (e.g., spatially matched) for data reception, as described below. Filtering). Modulator 216 performs modulation (eg, for orthogonal frequency division multiplexing (OFDM)) for data transmission. Demodulator 218 performs demodulation (eg, for OFDM) for data reception. The detection / acquisition unit 224 performs a process for detecting and acquiring a signal from the user terminal. Main controller 220 controls the operation of the various processing units within access point 110 and generates control for transceiver 230 and RFE 116. For example, the main controller 220 may include T i control signals used to enable and disable each transmitter unit 230, and enable and disable each receiver unit 260. It is also possible to generate R i control signals used for the purpose. The power controller 226 performs power management for the access point 110. For example, power controller 226 may determine whether to transmit DC power to RFE 116. RAM and ROM 222 store data and program codes used by various processing units in digital unit 210. For example, memory 222 may store the selected antenna set for each user terminal.

5A is an illustration of an embodiment of an RFE 116x that may be used for each RFE 116 shown in FIG. 1. RFE 116x may be used for a time division duplexing (TDD) communication system that transmits data on the downlink and uplink on the same frequency band at different times. In the embodiment shown in FIG. 5A, RFE 116x includes switches 510 and 540, power amplifier 520, low noise amplifier 530, and bandpass filter 550. The switches 510 and 540 receive a transmit / receive (T / R) control signal indicating whether an RF signal is being transmitted or received by the access point 110. Each switch couples its input to "T" outputs during the transmitter and "R" outputs during the receiver, as represented by the T / R control signal. The main controller 220 may generate a T / R control signal and provide this signal to each RFE 116 via an associated transceiver 230 (not shown in FIG. 4).

In the transmission path, the RF modulated signal from the associated transmitter unit 240 is received through the first port, routed through the switch 510, and amplified to a fixed gain or variable gain by the power amplifier 520. To obtain the desired output signal level. The amplified signal from power amplifier 520 is routed through switch 540 and filtered by filter 550 to remove out-of-band noise and unwanted signal components, and associated remote antennas through the second port. 114 is provided. In the receive path, the RF input signal from the associated remote antenna 114 is received through the second port, filtered by filter 550 to remove out-of-band noise and unwanted signal components, and switch 540 Routed and amplified by the LNA 530 to a fixed or variable gain. The amplified signal from the LNA 530 is routed through the switch 510 and provided to the associated receiver unit 260 through the first port.

The power amplifier 520 and / or LNA 530 may be powered down whenever possible to reduce power consumption. For example, the T / R control signal may power down the power amplifier 520 during the receiver and power down the LNA 530 during the transmitter. The RF signal, T / R control signal, and DC power may be provided by the access point 110 to the RFE 116x via cable 118, or by some other means.

FIG. 5B is a diagram illustrating an embodiment of an RFE 116y that may be used for each remote front end 116 shown in FIG. 1. RFE 116y may be used for a frequency division duplexing (FDD) communication system that can transmit data on the downlink and uplink simultaneously on different frequency bands. In the embodiment shown in FIG. 5B, RFE 116y includes duplexers 512 and 542, power amplifier 520, and LNA 530.

In the transmission path, the RF modulated signal from the associated transmitter unit 240 is received through the first port, filtered by the duplexer 512, routed to the power amplifier 520, and obtaining the desired output signal level. To be amplified to gain in order to be filtered by the duplexer 542 is provided to the associated remote antenna 114 through the second port. In the receive path, the RF input signal from the associated antenna 114 is received through the second port, filtered by the duplexer 542, routed to the LNA 530, amplified with a gain, and the duplexer 512. Is filtered and provided to the associated receiver unit 260 via the first port. No T / R control signal is needed for RFE 116y.

5A and 5B show particular embodiments of RFEs 116x and 116y, respectively. In general, the transmit path and receive path may each include one or more stages, such as an amplifier, a filter, and the like. The transmit path and receive path may also include fewer circuit blocks, different circuit blocks, and / or additional circuit blocks not shown in FIGS. 5A and 5B.

For clarity, the above description shows each remote antenna 114 coupled to the associated RFE 116, and each transceiver 230 processing the RF signal for one AP antenna. In general, each RFE 116 and / or each transceiver 230 may be associated with a set of one or more antenna elements. If an RFE or transceiver is associated with multiple antenna elements, these antenna elements may be viewed as a single (distributed) "antenna" for the RFE or transceiver.

In the WLAN 100, a “dummy” station may be deployed throughout the WLAN deployment area and used for various functions such as system configuration, calibration of transmitter and receiver electronics, antenna selection, and the like. These US states may be ininepensive stations with basic MAC / PHY functionality, and may not need all of the software required for a regular station.

Each US may transmit a training / pilot / sounding packet at a designated time or whenever directed by access point 110. The access point 110 may use the training packet to perform various functions. For example, the access point 110 may adjust the frequency response of the transmitter unit 240 and the receiver unit 260 of the transceivers 230a-230n and the frequency response of the RFE 116a-116m based on the training packet. have. If the United States is in a known location, the access point 110 may confirm the channel quality observed by the remote antenna 114 and may use the channel quality information for antenna selection.

An example scenario using the United States may be as follows. The United States may be strategically placed at the entrance and exit to the coverage area, for example at the entrance to a large office complex with many bedrooms and offices. Each US can transmit training packets to the access point, which can process these training packets to construct a transmit and receive eigenvector for the US. When a new station enters an office complex according to an active call already in progress, the handoff of the new station with the access point is precomputed from the nearest US that may be identified based on signal strength measurements. It may be simplified by using the eigenvectors. This can make handoff smooth and quick. Eventually, packets by packet transmission enable derivation of more optimal eigenvectors than new stations, but the United States will provide a reasonable starting point.

The WLAN 100 may support multiple transmission modes, such as, for example, no steering, beam steering, eigensteering, construction transmit diversity (STTD), spatial frequency transmit diversity (SFTD), and the like. Table 2 lists, for each transmission mode, the number of antennas used for data transmission and the number of antennas used for data reception. N ap is the total number of antennas available at the access point, and N ut is the total number of antennas available at the user terminal scheduled for downlink data transmission and uplink data transmission. In Table 2 and below, for each transmission mode, T is the number of antennas used by the access point for downlink data transmission of the user terminal using its respective transmission mode, and N is down The maximum number of antennas allowed by the WLAN for data transmission on the link and uplink, where S dn (where S dn ≤ min {N, N ut } and N ap > N) is determined by the access point by the user The number of data streams sent simultaneously to the terminal. In each transmission mode, R is the number of antennas used by the access point for receiving uplink data transmissions transmitted by the user terminal using its respective transmission mode, and S up is accessed by the user terminal. The number of data streams sent simultaneously to the point.

Figure 112008000167691-pct00002

The same or different transmission modes may be used for downlink and uplink data transmission between the access point and the user terminal. The access point may use the same or different set of antennas for downlink data transmission and uplink data reception. The spatial processing performed by the access point 110 for the transmission modes listed in Table 2 is described below.

Access point 110 may perform beamsteering to steer the downlink data transmission towards a particular user terminal x. The user terminal x may have a single antenna or may be the user terminal 120a or 120c of FIG. 1. Access point 110 selects a number T of antennas from among N ap antennas available for data transmission to user terminal x. A MISO channel is formed between the T antennas selected at access point 110 and a single antenna at user terminal x. This MISO is a 1xT channel response row vector for each subband k.

Figure 112008000167691-pct00003
Where j = 1, ..., T, h x , j (k) is the complex channel gain between the single UT antenna and the AP antenna j for subband k. Access point 110,

Figure 112008000167691-pct00004

For example, spatial processing may be performed for beamforming, wherein

Figure 112008000167691-pct00005
Is a data symbol to be transmitted to user terminal x on subband k,
Figure 112008000167691-pct00006
Is a vector of T transmit symbols transmitted from the T antennas selected at access point 110,
Figure 112008000167691-pct00007
Is the conjugate transpose, and K is the number of subbands used for data transmission.

Access point 110 may transmit S dn data streams simultaneously from up to N antennas to user terminal y. The user terminal y has a plurality of antennas (N ut ) and may be the user terminal 120b or 120d of FIG. 1. The access point 110 selects a number (T) of antennas from among N ap antennas available for downlink data transmission to user terminal y, where T = S dn for nonsteering . Access point 110,

Figure 112008000167691-pct00008

For example, spatial processing may be performed for non-steering, where

Figure 112008000167691-pct00009
Is a vector of S dn data symbols to be transmitted to user terminal y on subband k,
Figure 112008000167691-pct00010
Is a vector of T transmit symbols to be sent to the user terminal y from the T antennas selected over subband k for non-steering.

Access point 110 may perform eigensteering to transmit multiple data streams to user terminal y over an orthogonal spatial channel (or eigenmode). The MIMO channel is formed between the N ut antennas at user terminal y and the T antennas selected at access point 110. This MIMO is the N ut × T channel response matrix for subband k.

Figure 112008000167691-pct00011
It may also be characterized by,

Figure 112008000167691-pct00012

Where y y , i, j (k) for i = 1, ..., N ut and j = 1, ..., T, for user subband k, Is the complex channel gain between antenna i at and antenna j at access point 110. Channel response matrix

Figure 112008000167691-pct00013
Quot;

Figure 112008000167691-pct00014

It can also be diagonalized by eigenvalue decomposition, such as

Figure 112008000167691-pct00015
Is the unit matrix of eigenvectors,
Figure 112008000167691-pct00016
Is a diagonal matrix of eigenvalues for subband k.
Figure 112008000167691-pct00017
The diagonal element of
Figure 112008000167691-pct00018
Is an eigenvalue that represents the power gain for the S eigenmodes of where S ≦ min {T, N ut }. Eigenmodes may be viewed as orthogonal spatial channels. Access point 110,
Figure 112008000167691-pct00019
To send data through
Figure 112008000167691-pct00020
You can also use the eigenvectors (or columns) of. Access point 110,
Figure 112008000167691-pct00021
A maximum of S or S dn ≤ S data streams may be simultaneously transmitted through S eigenmodes.

Access point 110,

Figure 112008000167691-pct00022

For example, spatial processing may be performed for eigensteering, where

Figure 112008000167691-pct00023
Is a vector of T transmit symbols to be sent to the user terminal y from the T antennas selected over subband k for steering. Access point 110 may also be, for example, as shown in equation (1),
Figure 112008000167691-pct00024
By performing spatial processing for beam steering using the eigenvectors for the best eigenmodes of
Figure 112008000167691-pct00025
Data can also be transmitted via the best eigenmode of.

Access point 110 may transmit a single data stream from two antennas to a user terminal using STTD or SFDT. In the case of STTD, the access point 110 has two vectors, i.e., for each pair of data symbols s 1 and s 2 .

Figure 112008000167691-pct00026
, Where
Figure 112008000167691-pct00027
Represents complex conjugate,
Figure 112008000167691-pct00028
Represents transpose. Access point 110 is a vector from two antennas selected on one subband in a first symbol period.
Figure 112008000167691-pct00029
After transmitting the two coded symbols in the vector from the same two antennas on the same subband in the second symbol period
Figure 112008000167691-pct00030
Send two coded symbols at. In the case of SFDT, the access point 110 is a vector from two antennas selected on the first subband.
Figure 112008000167691-pct00031
After transmitting the two coded symbols in the vector over the second subband in the same symbol period
Figure 112008000167691-pct00032
Send two coded symbols at.

The access point 110 may use multiple R antennas for receiving uplink data transmissions from the user terminal. The access point 110 selects R antennas from among N ap available antennas, where R depends on the transmission mode used by the user terminal for uplink data transmission, as shown in Table 2. do. R may also be greater than N if supported by spatial processing at the access point. For a TDD system, the downlink and uplink may, for example, be such that the channel response for the uplink is equal to the transpose matrix of the channel response for the downlink.

Figure 112008000167691-pct00033
May be assumed to be inverse to

The symbols received at the access point 110 for uplink data transmission from a single antenna terminal x are

Figure 112008000167691-pct00034

It may also be expressed as, wherein

Figure 112008000167691-pct00035
Is a data symbol transmitted by user terminal x on subband k,
Figure 112008000167691-pct00036
Is a vector of R symbols received for user terminal x,
Figure 112008000167691-pct00037
Is a noise vector received at the access point 110.

Access point 110,

Figure 112008000167691-pct00038

You can also perform receiver matched filtering, such as

Figure 112008000167691-pct00039
Quot;
Figure 112008000167691-pct00040
Is an estimate of,
Figure 112008000167691-pct00041
Is
Figure 112008000167691-pct00042
Postprocessed noise observed by.

The symbols received at the access point 110 for uplink data transmission from the multi-antenna terminal y using non-steering or eigensteering are

Figure 112008000167691-pct00043

It may also be expressed as, wherein

Figure 112008000167691-pct00044
Is a vector of data symbols transmitted by user terminal y,
Figure 112008000167691-pct00045
Is a vector of transmit symbols for N ut antennas at user terminal y,
Figure 112008000167691-pct00046
Is the effective channel response matrix for the uplink,
Figure 112008000167691-pct00047
Is a vector of symbols received at access point 110 for user terminal y.
Figure 112008000167691-pct00048
Depends on the transmission mode used by user terminal y for uplink data transmission, e.g., if user terminal y performs eigensteering,
Figure 112008000167691-pct00049
If user terminal y performs non-steering,
Figure 112008000167691-pct00050
to be.

Access point 110,

Figure 112008000167691-pct00051

Receiver spatial processing, such as

Figure 112008000167691-pct00052
Is a spatial filter matrix for subband k,
Figure 112008000167691-pct00053
Is post-detection noise. The access point 110 may be of the following equations:

Figure 112008000167691-pct00054

Figure 112008000167691-pct00055

Figure 112008000167691-pct00056

Spatial Filter Matrix Using Any One of

Figure 112008000167691-pct00057
You can also derive, where
Figure 112008000167691-pct00058

Figure 112008000167691-pct00059

Figure 112008000167691-pct00060
Is an identity matrix,
Figure 112008000167691-pct00061
Is the deviation of the noise at the access point 110. Equation (10) is for the filtering technique matched for eigensteering, equation (11) is for the zero forcing technique, and equation (12) is for the minimum mean square error (MMSE) technique. It is about. Zero forcing and MMSE techniques may be used for non-steering and eigensteering transmission modes.

The symbol received at the access point 110 for uplink data transmission from the multi-antenna terminal y using STTD,

Figure 112008000167691-pct00062

Figure 112008000167691-pct00063

It may also be expressed as, wherein

Figure 112008000167691-pct00064
And
Figure 112008000167691-pct00065
Are two data symbols transmitted from two UT antennas y1 and y2 in two symbol periods over subband k using STTD,
Figure 112008000167691-pct00066
Is a vector of channel gains between each of the two UT antennas y1 and y2 and the R selected AP antennas,
Figure 112008000167691-pct00067
Is a vector of received symbols for subband k in two symbol periods,
Figure 112008000167691-pct00068
Is a noise vector for two symbol periods. R≥1 for STTD and SFTD transmission modes.

Access point 110,

Figure 112008000167691-pct00069

Figure 112008000167691-pct00070

2 data symbols,

Figure 112008000167691-pct00071
and
Figure 112008000167691-pct00072
You can also derive an estimate of, where
Figure 112008000167691-pct00073
And
Figure 112008000167691-pct00074
Are each,
Figure 112008000167691-pct00075
And
Figure 112008000167691-pct00076
Is an estimate of,
Figure 112008000167691-pct00077
And
Figure 112008000167691-pct00078
Are each,
Figure 112008000167691-pct00079
And
Figure 112008000167691-pct00080
Postprocessed noise observed by.

The multi-antenna station described herein may be implemented by various means. For example, the multi-antenna station and any functions described herein may be implemented in a combination of hardware, firmware, or software. The units used to make measurements for AP antennas, select antennas for data transmission and reception, and process data and signals include one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), and digital signals. Processing device (DSPD), programmable logic device (PLD), field programmable gate array (FPGA), processor, controller, microcontroller, microprocessor, RF integrated circuit (RFIC), designed to perform the functions described herein It may be implemented in other electronic units, or a combination thereof.

Antenna selection may be performed in hardware or software. In the case of a software implementation, antenna selection may be performed by a module (eg, procedure, function, etc.) that performs the functions described herein. The software code may be stored in a memory unit (eg, memory unit 222 of FIG. 4) and may be executed by a processor (eg, controller 220). The memory unit may be implemented within the processor or external to the processor, in which case it can be communicatively coupled with the processor by various means as is known in the art.

The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (36)

A plurality of antennas coupled to the multi-antenna station and comprising one or more remote antennas located away from the multi-antenna station; A controller for selecting a set of one or more antennas from among the plurality of antennas for data transmission to a terminal; And At least one transmitter unit for transmitting data to the terminal via the at least one set of antennas. The method of claim 1, The controller obtains measurements for the plurality of antennas and selects the set of one or more antennas based on the measurements. The method of claim 1, And one or more power detectors that measure power received at the plurality of antennas and provide power measurements for the plurality of antennas. The method of claim 3, wherein And the controller selects a predetermined number of antennas having the highest power measurement among the plurality of antennas. The method of claim 3, wherein The controller selects an antenna having a power measurement that is greater than a predetermined power threshold. The method of claim 1, The controller selects the set of one or more antennas based on a known position of the plurality of antennas. The method of claim 1, The controller selects the set of one or more antennas based on location information for the plurality of antennas. The method of claim 1, The controller selects a transmission mode from among a plurality of supported transmission modes, based on the number of antennas in the set, wherein the selected transmission mode is used for data transmission to the terminal. The method of claim 1, And a memory unit for storing the set of one or more antennas for the terminal and providing the set of one or more antennas for subsequent data transmission to the terminal. The method of claim 1, And the controller further selects a second set of one or more antennas among the plurality of antennas for reception of an uplink transmission from the terminal. The method of claim 10, The controller selects the second set of one or more antennas based on a transmission mode used by the terminal for the uplink transmission. The method of claim 10, The controller selects the set of one or more antennas used for data transmission to the terminal as the second set of one or more antennas used for reception of the uplink transmission from the terminal. soup. The method of claim 10, And at least one receiver unit for receiving the uplink transmission from the terminal via the second set of one or more antennas. The method of claim 1, One or more remote front ends coupled to the one or more remote antennas, each remote front end performing signal conditioning on radio frequency (RF) signals transmitted and received via an associated remote antenna; soup. The method of claim 1, And a radio frequency (RF) switch coupling the one or more transmitter units to the plurality of antennas. The method of claim 1, And the plurality of antennas comprises two or more remote antennas located away from the multi antenna station and distributed within a coverage area of the multi antenna station. The method of claim 1, Wherein at least two of the plurality of antennas have a different radiation pattern. Selecting a set of one or more antennas from among a plurality of antennas for data transmission from a multi-antenna station to the terminal, the plurality of antennas comprising one or more remote antennas located away from the multi-antenna station; Selecting a set of one or more antennas; And Transmitting data to the terminal via the set of one or more antennas. The method of claim 18, Obtaining measurements for the plurality of antennas. The method of claim 19, The step of selecting a set of one or more antennas, Selecting a predetermined number of antennas having the highest measurement among the plurality of antennas. The method of claim 19, The step of selecting a set of one or more antennas, Selecting an antenna having a measurement greater than a predetermined threshold. The method of claim 18, The step of selecting a set of one or more antennas, Selecting the set of one or more antennas based on location information for the plurality of antennas. The method of claim 18, Storing the set of one or more antennas for the terminal; And Using the stored set of one or more antennas for subsequent data transmission to the terminal. The method of claim 18, Selecting a second set of one or more antennas from the plurality of antennas for receiving uplink transmissions from the terminal; And Receiving the uplink transmission via the second set of one or more antennas. As a data transmission device, Means for selecting a set of one or more antennas from among a plurality of antennas for data transmission to a terminal, the plurality of antennas comprising one or more remote antennas positioned away from the data transmission device. Set selection means; And Means for transmitting data to the terminal via the set of one or more antennas. The method of claim 25, And means for obtaining measurements for the plurality of antennas. The method of claim 26, The means for selecting a set of one or more antennas, Means for selecting a predetermined number of antennas having the highest measurement among the plurality of antennas. The method of claim 26, The means for selecting a set of one or more antennas, Means for selecting an antenna having a measurement larger than a predetermined threshold. The method of claim 25, Means for storing the set of one or more antennas for the terminal; And Means for using the stored set of one or more antennas for subsequent data transmission to the terminal. The method of claim 25, Means for selecting a second set of one or more antennas among the plurality of antennas for receiving uplink transmissions from the terminal; And And means for receiving the uplink transmission via the second set of one or more antennas. A computer readable medium containing instructions for transmitting data, the computer readable medium comprising: The command is Selecting a set of one or more antennas from among a plurality of antennas for data transmission from a multi-antenna station to the terminal, wherein the plurality of antennas comprises one or more remote antennas located away from the multi-antenna station; A set selection command of one or more antennas; And Instructions for transmitting data to the terminal via the set of one or more antennas. The method of claim 31, wherein Further comprising instructions for obtaining measurements for the plurality of antennas. 33. The method of claim 32, The set selection command of the one or more antennas, And selecting a predetermined number of antennas having the highest measurement among the plurality of antennas. 33. The method of claim 32, The set selection command of the one or more antennas, And selecting an antenna having a measurement that is greater than a predetermined threshold. The method of claim 31, wherein The set selection command of the one or more antennas, And selecting the set of one or more antennas based on location information for the plurality of antennas. The method of claim 31, wherein Selecting a second set of one or more antennas among the plurality of antennas for receiving uplink transmissions from the terminal; And And receiving the uplink transmission via the second set of one or more antennas.
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KR20150046023A (en) * 2012-07-20 2015-04-29 에이디씨 텔레커뮤니케이션스 인코포레이티드 Integration panel
KR101631197B1 (en) 2012-07-20 2016-06-16 에이디씨 텔레커뮤니케이션스 인코포레이티드 Integration panel

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